1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording information by discharging ink from recording means to a recording member.
2. Related Background Art
A recording apparatuses, each of which is used as an output apparatus for a recording apparatus having functions of a printer, a copying machine and a facsimile machine and the like or combined-type electronic equipment including a computer and a word processor and a work station, are arranged so that an image is recorded on a recording member (a recording medium), such as paper or a thin plastic sheet, in accordance with image information (character information included). The recording apparatuses of the foregoing type are categorized into ink jet recording apparatuses, wire dot recording apparatuses, thermal recording apparatuses and laser beam recording apparatuses and the like depending upon the recording method.
A serial-type recording apparatus adapted to a serial scan method, in which main scanning is performed in a direction that intersects a direction (a sub-scanning direction) in which a recording member is conveyed, is so arranged that information is recorded on the entire surface of the recording member by repeating the following steps of: setting the recording medium to a predetermined recording position; using recording means mounted on a carriage, which is moved along the recording member, to record (main-scan) an image until information for line is recorded; conveying paper by a predetermined quantity (conveyance of recording member); and image for the next line is recorded (main-scanned) on the recording member which has been again stopped. A line-type recording apparatus which records information by one sub-scanning in the conveyance direction of the recording member is so arranged that information is recorded on the entire surface of the recording member by the following steps of: setting the recording medium to a predetermined recording position; and continuously conveying (pitch conveying) the paper while collectively recording information for one line.
Among the foregoing various recording apparatuses, a recording apparatus (an ink jet recording apparatus) adapted to the ink jet recording method records information by discharging ink from recording means (a recording head) to a recording member and exhibits advantages that recording means can be compactized, a precise and excellent image can be recorded at high speed, the image can be recorded on plain paper without special treatment, the running cost can be reduced, noise can be satisfactorily eliminated because of the employed non-impact method, and a color image can be easily recorded by making use of multiple-color inks. In particular, a line-type recording apparatus using a full-multiple-type recording means having a multiplicity of discharge ports in the widthwise direction of the paper enables the recording operation to be performed at a higher speed.
Particularly, the ink-jet recording means (recording head) making use of heat energy to discharge ink is able to easily comprise fluid passage (configuration of discharge ports) formed precisely by forming an electrothermal converter, electrodes, the fluidpassage walls and a ceiling plate on the substrate by semiconductor manufacturing processes comprising the etching, evaporating and sputtering operations. Therefore, the size can be further reduced. Further, the recent trend of using recording members made of various materials arises a need to use a thin paper sheet and a fabric paper sheet (paper having filing punch apertures, perforated paper and paper formed into an arbitrary shape) as well as the paper and the thin resin sheet (OHP and others) which are conventional recording members.
The ink jet recording apparatus comprises a cap for capping the discharge port for use at the time of a suction recovery operation for overcoming defective discharge by sucking ink from the discharge port and for preventing the problem that the ink is dried at the discharge port. If bubbles, that cannot be eliminated at the time of the ink discharge, are excessively introduced into the discharge port or if the volume of the bubbles has been enlarged excessively, there sometimes arises a problem that the discharge port is undesirably clogged and, accordingly, the ink passage cannot be maintained. In order to eliminate the bubbles, the foregoing suction recovery operation is usually performed.
The color ink jet recording apparatus having a plurality of recording heads, for example, four-color-recording heads composed of black, cyan, magenta and yellow recording heads comprises a suction recovery system which includes a plurality (four) of caps and a plurality (four) of suction pumps connected to the caps, or another system which includes a plurality (four) of caps and one suction pump connected to the caps. As a result, all recording heads can be operate at the time timing to recover the suction.
Further, the ink jet recording apparatus encounters a problem of deterioration of the image quality due to the deviation of the ink discharging direction if ink undesirably adheres to the surface (the surface in which the discharge ports are disposed) of the discharge port of the recording head (recording means). That is, since the ink jet recording method is so arranged that ink droplet is discharged from the recording head on to the paper or the OHP film to record an image, fine flowing ink droplets generated in addition to the discharged main ink droplet or ink droplets allowed to reach and rebound from the recording member adhere to the surface of the discharge port causing the surface to be wetted. If the adhered ink gathers in the vicinity of the discharge port, problems arise in that the ink is discharged into an undesirable direction (deviation) or the ink discharge cannot be performed (no discharge).
The ink jet recording apparatus comprises means for overcoming the foregoing problem occurring due to the use of a fluid (the ink) as the recording agent to restore or maintain the surface of the discharge port at a satisfactory state, the means being restoring means (a restoring system) for the recording head. As means for refreshing the surface of the discharge port and preventing the deviation of the discharging direction, there has been used a wiping member arranged to be contact with the surface of the discharge port to enable the two elements to be moved mutually so as to wipe out (perform wiping) foreign matters such as ink droplets.
The undesirable ink droplet caused to adhere to the surface of the discharge port is also generated from ink mist generated at the time of the ink discharge to be performed at the time of the recording operation and rebound of ink from the paper. The mutual approaching movement performed by the recording head and the paper during the recording operation sometimes causes foreign matters such as paper dust to adhere to the surface of the discharge port. Therefore, the ink droplet and the foreign matter present on the surface of the discharge port are usually removed by the foregoing wiping means during or after the recording operation.
The wiping means is usually structured in such a manner that a blade made of an elastic material such as rubber wipes out the surface of the discharge port to remove the undesirable ink droplet. However, the performance of the foregoing wiping means deteriorates due to use for a long time of a temporary increase in the ink to be wiped out. Therefore, the discharging performance of the wiping means cannot easily be maintained. What is worse, ink deposited on the blade serving as the wiping means and having increased viscosity or a foreign matter is shifted reversely to the surface of the discharge port, causing a problem to occur in that the discharge cannot be performed due to the deviation of the discharging direction and embedding of the foreign matter.
Another problem sometimes arises when the surface of the discharge port of the recording head is wiped out in that a portion of the wiped ink flies in the recording apparatus due to the elasticity of the blade and the portion inside the apparatus is contaminated. What is worse, a major portion of the ink which has not flied and which is left on the blade or foreign matters such as paper dust are allowed to adhere to the blade as it is. The evaporation of the ink left on the blade increases the viscosity of the ink. Further, the foreign matter, such as the paper dust, is allowed to firmly adhere and deposits, the foreign matter being then inversely moved to the surface of the discharge port. As a result, the problems of the no-discharge and the directional deviation sometimes arise.
If two or more recording heads (the recording means) are used simultaneously and inks of a plurality of colors are used to record color images, the ink moved to the blade at the first wiping operation is mixed with a different-color ink of the recording head at the time of wiping out the recording head for the different color. In this case, the quality of the image sometimes deteriorates. Further, in the color ink jet recording apparatus, wiping of a plurality of recording heads by using one blade causes the quantity of ink allowed to adhere to the blade to be increased. Therefore, the adverse influence of the contamination of the blade becomes critical. Although it might therefore be feasible to employ a structure in which an exclusive blade is provided for each recording head, other problem arises in that the cost cannot be reduced and an excessively large installation space is required.
In order to prevent the foregoing deterioration in the wiping performance, it has been suggested that cleaning means for cleaning the wiping means is provided. As an optimum and most ordinary structure of the cleaning means, a structure using porous ink absorber exhibiting excellent ink absorbing performance has been employed. The ink absorber of the foregoing type comes in contact with the blade or the like serving as the wiping means to move mutually as to remove the foreign matter allowed to adhere to the blade by rubbing and as to absorb the ink so that the blade can be cleaned. However, the ink absorbing performance of an ink absorber even having excellent cleaning performance sometimes deteriorates as it absorbs the ink. Therefore, it is difficult to maintain the reliability for a long time.
As the case where the ink adheres to the surface of the discharge port, there is a case where the ink discharged from the fluid passage by a pump or the like adheres to the surface of the discharge port. Further, the ink jet recording apparatus sometimes encounters a problem that the viscosity of the ink in the fluid passage is increased due to evaporation of water or the like and the discharge cannot be enabled even if discharging force is supplied. Therefore, a suction pump has been usually used to forcibly discharge the ink, which is not suitable to be discharged and to refresh the ink in the fluid passage. In this case, the quantity of the ink allowed to adhere after the suction operation is sometimes larger than the quantity of ink allowed to adhere during the recording operation. In such a case, the load which must be borne by the wiping means becomes excessively heavy.
FIGS. 1A to 1D are schematic cross sectional views which illustrate the operation of a cap at the time of the suction recovery operation. FIG. 1A illustrates a capping state (a capping state realized in such a manner that a cap 103 is brought into contact in a hermetical manner with a discharge port surface 102 of a recording head 101, and a suction pump (omitted from illustration) connected to the cap 103 is used to generate vacuum pressure to suck out the ink from the discharge port, the capping state being a state in which the pressure has been recovered (a state in which the pressure has been so recovered as not to break the meniscus of the discharge port). A diagonal portion 104 shown in FIGS. 1A to 1D designates the sucked ink. In the state shown in FIG. 1A, the inside portion of the cap 103 is considered to be substantially filled with ink.
If the cap 103 is intended to be removed from the capping state shown in FIG. 1A, force for upwards sucking the ink due to the adhesive force of the ink and the negative pressure in the discharge port acts on the boundary between the discharge port surface 102 and the ink 104. Further, a surface tension of the cohesive force of the ink itself acts on the ink in the cap 103. Therefore, draw-downs 105 occur in the ink 104, the cross section of each draw-downs 105 of the ink 104 being reduced as the cap 103 is separated. Therefore, the portion of the draw-down 105 is made most weaken.
Finally, the ink is disconnected at each draw-down 105 as shown in FIG. 1D, resulting in that a portion of the ink is left on the discharge port surface 102. The quantity of the ink left on the discharge port surface 102 at this time is larger than the quantity of the ink allowed to adhere due to mist and realized during the recording operation. The quantity of the left ink tends to be enlarged in inverse proportion to the surface tension of the ink and also in inverse proportion to the water repellency of the discharge port surface 102. The load, that must be borne by the wiping blade and the wiping cleaner, is enlarged in proportion to the quantity of the ink allowed to adhere to the discharge port surface 102. As a result, the life of each of the wiping element is shortened. Other problems of falling and flying of the ink arise in the case shown in FIGS. 1A to 1D because the ink is left in the cap 103 when the cap 103 is removed.
When the cap 103 is immediately removed after the ink has been sucked, the atmospheric pressure instantaneously acts on the portion inside the cap in which the negative pressure is left. The rapid pressure change and the mechanical impact at the time of the removal break the meniscus in the discharge port, causing air to be introduced deeply into the discharge port. In this case, the ink discharge is sometimes made defective.
The suction recovery operation of the conventional ink jet recording apparatus is performed by making use of a cylinder pump which does not use the gravity of the ink, which makes use of the movement of a piston thereof and which is capable of assuredly restore ink even if it is disposed horizontally. The cylinder pump is arranged in such a manner that the surface of the cylinder pump opens/closes an aperture for restoring waster ink from an ink receiving member, such as the cap, to move the waste ink to a waster-ink accommodating portion having an ink capacity larger than the ink receiving member via a waste ink movement passage formed adjacent to the shaft of the piston.
However, the suction recovery means of the conventional ink jet recording apparatus using a plurality of recording heads, such as the color recording heads, has comprised the caps corresponding to the respective recording heads and suction pumps correspond to the caps. As an alternative to this, a structure has been employed which comprises caps corresponding to the recording heads and a large suction pump connected to all caps are provided. Further, the suction recovery operations for all of the plural recording heads are performed at the same timing. Therefore, the quantity of the waste ink increases in proportion to the number of the recording heads and, accordingly, the waste ink accommodating portion must have a large size in proportion to the quantity of the waste ink. As a result, a problem arises in that the size of the recording apparatus cannot be reduced.
The fact that the operations for recovering the suction of all recording heads are performed at the same timing causes the ink to be sucked from a recording head that does not need to be sucked due to the frequencies of use of each recording head and the characteristics of the ink. Therefore, the ink is undesirably consumed. The undesirable consumption of the ink give a user (user which mainly performs monochrome recording operations), which mainly uses a specific recording head, that the ink, which has not been used so frequently, is decreased.
In order to overcome the problem of a type of the defective ink discharge, a method disclosed in, for example, Japanese Patent Appln. Laid-Open No. 60-151059, has been employed which has an arrangement that the cap and an air inlet valve are, by a tube, connected to each other, the air inlet valve is opened to cause the inside portion of the cap to communicate with the atmosphere to suck the ink left in the cap, and then the cap is separated. However, the recent trend of reducing the size of the ink jet recording apparatus arises a necessity of reducing the size of the cap and that of its peripheral mechanisms. Therefore, it is difficult to dispose the foregoing air-inlet valve in the small cap. What is worse, dust is undesirably introduced into the tube for establishing the connection with the air inlet valve, causing the operation to be prevented.
Further, a certain level of negative pressure is needed to discharge the dust allowed to adhere to the discharge port surface, bubbles in the discharge port and the ink having a raised viscosity. Therefore, the foregoing structure in which the air inlet valve is provided in the cap causes the size of the cap to be enlarged. As a result, a problem accordingly arises in that the quantity of the ink to be sucked cannot be reduced. If the quantity of the ink to be sucked is too large, the quantity of the waste ink and the running cost cannot be reduced.
The foregoing serial-type ink jet recording apparatus comprises, in the vicinity of the home position for the carriage, the cleaning means for cleaning the recording head as well as the protecting cap. Therefore, the serial ink jet recording apparatus encounters a problem in that the width of the apparatus cannot be narrowed and the size and the weight of the apparatus cannot therefore be reduced. In a particular case where the cleaning means comprises a plurality of mechanisms, such as the suction recovery mechanism, the wiper mechanism and the sub-discharge mechanism and the like, the foregoing problems become more critically. What is worse, the distance for which the carriage must be moved at the time of the cleaning operation cannot be shortened, causing a problem to arise in that the through put at the time of the recording operation deteriorates.
When a color recording operation or a gradient image recording operation is performed with the foregoing recording apparatus, a plurality of recording heads corresponding to the colors to be recorded and the recording density have been used. The serial type recording apparatus comprising a plurality of recording heads is adapted to a method in which the plural recording heads are mounted on a movable member (a carriage), and the respective recording head are, in response to predetermined image signals, driven sequentially starting from the head disposed in the upstream of the moving direction while moving the movable member to record image on a recording member.
The serial recording apparatus must have a predetermined approaching width to act from the moment at which the movement of the movable member is commenced to a moment at which the recording head commences the recording operation. That is, a first transition region (the approaching width), in which the speed of the movable member reaches a predetermined speed from a stopped state, must be disposed between a main scanning portion (the ink discharge portion in a case where the ink jet recording head is used) for the recording operation to be performed by the recording head at the point at which the movable member commences its movement and the end of the recording member on the same side.
The recording head comprises a main scanning portion for the recording operation, such as the discharge port portion adapted to the ink jet recording method, or a heating element portion adapted to the thermal recording method or a dot wire portion adapted to the wire dot recording method. The recording head is formed into a horizontally symmetrical shape with respect to the main scanning portion for the recording operation or formed into asymmetrical with respect to the main scanning portion for the recording operation. The asymmetrical recording head requires right and left spaces which are different in size with respect to the main scanning portion for the recording operation.